An animal some authors entertain (5)
I believe the answer is:
horse
'an animal' is the definition.
(type of animal)
'some authors entertain' is the wordplay.
'some' indicates a hidden word (some parts of the word are used).
'HORSE' is hidden in the letters of 'authors entertain'.
(Other definitions for horse that I've seen before include "Eg, mare" , "Equid" , "It may get people stoned" , "Vaulting --; -- sense" , "Vaulting apparatus" .)